Don't worry quite so much about the eGFR. The "e" stands for estimated. It is based on an assumed body size. It can vary a great deal depending on how hydrated/dehydrated he is when he has his labwork done. Yes, his function probably slipped, but it may pop up somewhat again. That is the nature of the best - the levels go up and down. Watch for trends over longer periods of time. Don't get too excited if it looks like things are improving, and don't get too upset if they drop. It is typically a long, slow process.